Subclassification of patients with acute myelogenous leukemia based on chemokine responsiveness and constitutive chemokine release by their leukemic cells

BACKGROUND AND OBJECTIVES

Chemokines are soluble mediators involved in angiogenesis, cellular growth control and immunomodulation. In the present study we investigated the effects of various chemokines on proliferation of acute myelogenous leukemia (AML) cells and constitutive chemokine release by primary AML cells.

DESIGN AND METHODS

Native human AML cells derived from 68 consecutive patients were cultured in vitro. We investigated AML cell proliferation (3H-thymidine incorporation, colony formation), chemokine receptor expression, constitutive chemokine release and chemotaxis of normal peripheral blood mononuclear cells.

RESULTS

Exogenous chemokines usually did not have any effect on AML blast proliferation in the absence of hematopoietic growth factors, but when investigating growth factor-dependent (interleukin 3 + granulocyte-macrophage colony-stimulating factor + stem cell factor) proliferation in suspension cultures the following patient subsets were identified: (i) patients whose cells showed chemokine-induced growth enhancement (8 patients); (ii) divergent effects on proliferation (15 patients); and (iii) no effect (most patients). These patient subsets did not differ in chemokine receptor expression, but, compared to CD34- AML cells, CD34+ cells showed higher expression of several receptors. Chemokines also increased the proliferation of clonogenic AML cells from the first subset of patients. Furthermore, a broad constitutive chemokine release profile was detected for most patients, and the following chemokine clusters could be identified: CCL2-4/CXCL1/8, CCL5/CXCL9-11 (possibly also CCL23) and CCL13/17/22/24/CXCL5 (possibly also CXCL6). Only the CCL2-4/CXCL1/8 cluster showed significant correlations between corresponding mRNA levels and NFkB levels/activation. The chemotaxis of normal immunocompetent cells for patients without constitutive chemokine release was observed to be decreased.

INTERPRETATION AND CONCLUSIONS

Differences in chemokine responsiveness as well as chemokine release contribute to patient heterogeneity in AML. Patients with AML can be classified into distinct subsets according to their chemokine responsiveness and chemokine release profile.

Regulation of constitutive STAT5 phosphorylation in acute myeloid leukemia blasts

In the present study, we examined the underlying mechanism, which causes the constitutive tyrosine phosphorylation of signal transducer and activator of transcription 5 (STAT5) in acute myeloid leukemia (AML) blasts. Constitutive STAT5 phosphorylation was observed in 18 of 26 (69%) patients with AML. The constitutive STAT5 phosphorylation was caused by different mechanisms. In the majority of the investigated cases (71% (12 of 17)) constitutive STAT5 phosphorylation was associated with autophosphorylation of the type III receptor tyrosine kinase Flt3. In 47% (eight of 17) of these cases autophosphorylation of Flt3 coincided with tandem duplications of the Flt3 gene, resulting in constitutive phosphorylation of the receptor, while 24% (four of 17) of the cases demonstrated STAT5 phosphorylation and Flt3 autophosphorylation without mutations. In addition, a subset of AML cases (29% (five of 17)) had no autophosphorylation of the Flt3 receptor, but demonstrated constitutive STAT5 phosphorylation, which was partly due to autocrine growth factor production. All AML cases with high STAT5 and Flt3 phosphorylation demonstrated, in general, a lower percentage of spontaneous apoptosis, compared to AML blasts with no spontaneous STAT5 phosphorylation. Addition of the receptor tyrosine III kinase inhibitor AG1296 strongly inhibited STAT5 phosphorylation and enhanced the percentage of apoptotic cells without modulating the Bcl-xl protein levels. These data indicate that in the majority of AML cases the constitutive STAT5 phosphorylation is caused by Flt3 phosphorylation mostly due to mutations in the receptors and associated with a low degree of spontaneous apoptosis.

Heterogeneous CD52 Expression among Hematologic Neoplasms: Implications for the Use of Alemtuzumab (CAMPATH-1H)

PURPOSE

CD52 is a GPI-linked glycoprotein expressed by B cells, T cells, monocytes, and macrophages. The humanized monoclonal antibody alemtuzumab (CAMPATH-1H) is specific for CD52 and is Food and Drug Administration - approved for the treatment of relapsed or refractory chronic lymphocytic leukemia (CLL). The utility of CAMPATH in the treatment of other hematologic neoplasms has been explored; however, a comprehensive survey of CD52 expression among a broad spectrum of WHO-defined tumor types has not been completed.

EXPERIMENTAL DESIGN

We evaluated 294 hematologic neoplasms for the presence of CD52 using standard immunohistochemical techniques on paraffin-embedded biopsy specimens fixed with formalin, B-Plus, Zenker's acetic acid, or B5-formalin.

RESULTS

The vast majority of low-grade B cell lymphoproliferative disorders (CLL/small lymphocytic leukemia, follicular lymphoma, lymphoplasmacytic lymphoma, hairy cell leukemia, and mucosa-associated lymphoid tissue lymphomas) express CD52. In addition, we found that the majority of precursor B cell acute lymphoblastic leukemia/lymphomas express this antigen. In contrast, there is surprising heterogeneity in CD52 expression among more aggressive B cell lymphomas, with 25% of cases of diffuse large B cell lymphoma and Burkitt lymphoma demonstrating no detectable CD52. In addition, the majority of neoplasms of the T cell lineage are negative for the antigen, including most cases of precursor T cell acute lymphoblastic leukemia/lymphoma, anaplastic large cell lymphoma, and peripheral T cell lymphoma, not otherwise specified. Finally, the vast majority of cases of acute myeloid leukemia, Hodgkin lymphoma, and multiple myeloma are negative for CD52 expression.

CONCLUSION

In contrast with CLL, the variable expression of CD52 among other hematologic malignancies suggests that target validation on a case-by-case basis will likely be necessary to guide the rational analysis of CAMPATH therapy.

Constitutive NF-kappaB DNA-binding activity in AML is frequently mediated by a Ras/PI3-K/PKB-dependent pathway

In the present study, we aimed to elucidate the mechanism responsible for constitutive NF-kappaB DNA-binding activity in AML cells. Intervening in aberrant signaling pathway provides a rational approach for in vivo targeting of AML cells. Constitutive NF-kappaB DNA-binding activity was observed in 16 of 22 (73%) investigated AML cases and was, in general, associated with resistance to spontaneous apoptosis. Indeed, inhibition of NF-kappaB activity by the NF-kappaB inhibitor SN-50 peptide resulted in enhanced chemotherapy-induced apoptosis. In the majority of cases, constitutive NF-kappaB activity was mediated by a Ras/PI3 kinase (PI3-K)/protein kinase B (PKB)-mediated pathway. The PI3-K inhibitor Ly294002 and the Ras inhibitor L-744832 both inhibited PKB phosphorylation and NF-kappaB DNA-binding activity. The constitutive activation of Ras GTP-ase was caused by mutations in the gene encoding for N-Ras in 29% of the cases. The constitutive NF-kappaB activity could so far not be ascribed to the autocrine production of growth factors or to mutations in the Flt3 receptor, since anti-GM-CSF, -IL-1, -IL6, -TNFalpha or the tyrosine kinase inhibitor AG1296 did not affect the NF-kappaB DNA-binding activity. The present study demonstrates that Ras activation is an important pathway for triggering the NF-kappaB pathway in AML cells.

A novel EVI1 gene family, MEL1, lacking a PR domain (MEL1S) is expressed mainly in t(1;3)(p36;q21)-positive AML and blocks G-CSF-induced myeloid differentiation

We have identified a novel gene MEL1 (MDS1/EVI1-like gene 1) encoding a zinc finger protein near the breakpoint of t(1; 3)(p36;q21)-positive human acute myeloid leukemia (AML) cells. Here, we studied the structure, expression pattern, and function of MEL1 in leukemia cells. In this study, we have identified 3 transcription start sites, 1 in exon 1 and 2 in exon 2, and 2 kinds of translation products, 170 kDa (MEL1) and 150 kDa (MEL1S). Notably, the 150-kDa band of MEL1S was detected mainly in the t(1;3)(p36;q21)-positive AML cells. By immunoblot analysis and proteolytic mapping, it is suggested that the 150-kDa band of MEL1S in the leukemia cells is translated from the internal initiation codon ATG597 in exon 4 and is mostly lacking the amino-terminal PR domain of MEL1. By the cyclic amplification and selection of targets (CASTing) method for identifying consensus sequences, it was shown that the consensus sequences of MEL1 were included in 2 different consensus sequences for DNA-binding domain 1 and 2 (D1-CONS and D2-CONS) of EVI1. In reporter gene assays, MEL1S activated transcription via binding to D2-CONS; however, the fusion of MEL1 or MEL1S to GAL4 DNA-binding domain (DBD) made them GAL4 binding site-dependent transcriptional repressors. Moreover, overexpression of MEL1S blocked granulocytic differentiation induced by granulocyte colony-stimulating factor (G-CSF) in interleukin-3 (IL-3)-dependent murine myeloid L-G3 cells, while MEL1 could not block the differentiation. Thus, it is likely that overexpression of the zinc finger protein lacking the PR domain (EVI1 and MEL1S) in the leukemia cells is one of the causative factors in the pathogenesis of myeloid leukemia.

Transcriptional regulation of globin gene expression in the human erythroid cell line K562

The effect of hemin on the rate of synthesis and the level of globin messenger RNA's in the human erythroid cell line K562 was examined by means of cloned hybridization probes specific for each of the human embryonic, fetal, and adult globin genes. Hemin increases both the rate of transcription and the level of accumulation of zeta-, epsilon-, gamma-, and alpha-globin messenger RNA's by a factor of 3 to 5. Thus, hemin induction of globin gene expression in K562 cells is at the level of transcription.

Expression of Bcl-2-related genes in normal and AML progenitors: changes induced by chemotherapy and retinoic acid

The expression of Bcl-2 family members was examined in normal and leukemic hematopoietic cells. Immature hematopoietic progenitor cells (CD34+/33-/13-) did not express Bcl-2 but Bcl-XL, the majority of CD34 cells expressed Bcl-2, Bcl-XL and BAD, and normal promyelocytes (CD34-/33+) lacked expression of both Bcl-2 and Bcl-XL, while leukemic CD34+progenitors and promyelocytes expressed these anti-apoptotic proteins. In AML, Bcl-2 expression was higher on CD34+ than on all AML cells, however, expression of Bcl-2 or Bcl-XL did not predict achievement of complete remission. Surprisingly, low Bcl-2 content was associated with poor survival in a group of patients with poor prognosis cytogenetics. The anti-apoptotic BAD protein was found to be expressed in AML, but was phosphorylated in 41/42 samples. Phosphorylation was found at both sites, Ser 112 and Ser 136. During induction chemotherapy, Bcl-2 levels of CD34 cells increased significantly. In the context of evidence for small numbers of leukemic CD34+ cells expressing very high levels of Bcl-2 prior to therapy, this finding is interpreted as a survival advantage of Bcl-2 overexpressing progenitors and rapid elimination of cells with low Bcl-2. Bcl-2 and Bcl-XL were both expressed in minimal residual disease cells. Downregulation of Bcl-2 mRNA and protein was observed by ATRA and the combination of Ara-C, followed by ATRA, resulted in markedly increased cytotoxicity in HL-60 cells, as compared to Ara-C alone or ATRA followed by Ara-C. Implications of these findings for the development of new therapeutic strategies for AML are discussed.

The oral iron chelator deferasirox represses signaling through the mTOR in myeloid leukemia cells by enhancing expression of REDD1

To evaluate the effect of deferasirox in human myeloid leukemia cells, and to identify the molecular pathways responsible for antiproliferative effects on leukemia cells during chelation therapy, we performed gene expression profiling to focus on the pathway involved in the anticancer effect of deferasirox. The inhibitory concentration (IC50) of deferasirox was 17-50 microM in three human myeloid cell lines (K562, U937, and HL60), while those in fresh leukemia cells obtained from four patients it varied from 88 to 172 microM. Gene expression profiling using Affymerix GeneChips (U133 Plus 2.0) revealed up-regulation of cyclin-dependent kinase inhibitor 1A (CDKN1A) encoding p21CIP, genes regulating interferon (i.e. IFIT1). Pathways related to iron metabolism and hypoxia such as growth differentiation factor 15 (GDF-15) and Regulated in development and DNA damage response (REDD1) were also prominent. Based on the results obtained from gene expression profiling, we particularly focused on the REDD1/mTOR (mammalian target of rapamycin) pathway in deferasirox-treated K562 cells, and found an enhanced expression of REDD1 and its down-stream protein, tuberin (TSC2). Notably, S6 ribosomal protein as well as phosphorylated S6, which is known to be a target of mTOR, was significantly repressed in deferasirox-treated K562 cells, and REDD1 small interfering RNA restored phosphorylation of S6. Although iron chelation may affect multiple signaling pathways related to cell survival, our data support the conclusion that REDD1 functions up-stream of tuberin to down-regulate the mTOR pathway in response to deferasirox. Deferasirox might not only have benefit for iron chelation but also may be an antiproliferative agent in some myeloid leukemias, especially patients who need both iron chelation and reduction of leukemia cells.

Adult biphenotypic acute leukaemia: an entity with poor prognosis which is related to unfavourable cytogenetics and P-glycoprotein over-expression

Biphenotypic acute leukaemia (BAL) patients represented 8% of the 287 de novo consecutive adult acute leukaemias (23 BAL, 230 acute myeloid leukaemia (AML) and 34 acute lymphoblastic leukaemia (ALL)) referred to our department during the last 4-year period. Of these 23 BAL patients, 14 patients showed myeloid morphology and nine cases lymphoid morphology according to FAB criteria. There were no differences between lymphoid and myeloid BAL according to clinical and biological presentation and treatment outcome. We confirm the poor prognosis of BAL when compared to AML or ALL seen during the same period of time, in terms of complete remission (47%, 62% and 82% respectively, BAL v AML, NS and BAL v ALL, P = 0.006) and 4-year overall survival (8.1%, 25.8% and 23.8% respectively, BAL v AML, P = 0.05 and BAL v ALL, P = 0.003). Comparing adult BAL patients with AML patients, we found an increase in poor prognostic factors: CD34+ phenotype (82% v 60% respectively, P = 0.03), unfavourable karyotype (60% v 20%, P < 0.0001) and Pgp over-expression by RT-PCR (0.705 v 0.107, P < 0.0001) and flow cytometry (0.824 v 0.391, P = 0.0001). MRP and LRP were not found to be poor prognostic factors. Comparing BAL patients with ALL patients, we found also an increase in poor prognostic factors: age (51 v 39, P = 0.003) and CD34+ phenotype (82% v 50%, P = 0.02). We conclude that BAL patients need a more aggressive treatment procedure, including high-dose AraC or the use of Pgp modulators for first-line therapy.

Interplay of RUNX1/MTG8 and DNA Methyltransferase 1 in Acute Myeloid Leukemia

The translocation t(8;21)(q22;q22) in acute myeloid leukemia (AML) results in the expression of the fusion protein RUNX1/MTG8, which in turn recruits histone deacetylases (HDAC) to silence RUNX1 target genes [e.g., interleukin-3 (IL-3)]. We previously reported that expression of the RUNX1/MTG8 target gene IL-3 is synergistically restored by the combination of inhibitors of HDACs (i.e., depsipeptide) and DNA methyltransferases (DNMT; i.e., decitabine) in RUNX1/MTG8-positive Kasumi-1 cells. Thus, we hypothesized that DNMT1 is also part of the transcriptional repressor complex recruited by RUNX1/MTG8. By a chromatin immunoprecipitation assay, we identified a RUNX1/MTG8-DNMT1 complex on the IL-3 promoter in Kasumi-1 cells and in primary RUNX1/MTG8-positive AML blasts. The physical association of RUNX1/MTG8 with DNMT1 was shown by coimmunoprecipitation experiments. Furthermore, RUNX1/MTG8 and DNMT1 were concurrently released from the IL-3 promoter by exposure to depsipeptide or stabilized on the promoter by decitabine treatment. Finally, we proved that RUNX1/MTG8 and DNMT1 were functionally interrelated by showing an enhanced repression of IL-3 after coexpression in 293T cells. These results suggest a novel mechanism for gene silencing mediated by RUNX1/MTG8 and support the combination of HDAC and DNMT inhibitors as a novel therapeutic approach for t(8;21) AML.

Pharmacologic inhibition of CDK4/6: mechanistic evidence for selective activity or acquired resistance in acute myeloid leukemia

Entry into the cell cycle is mediated by cyclin-dependent kinase 4/6 (CDK4/6) activation, followed by CDK2 activation. We found that pharmacologic inhibition of the Flt3 internal tandem duplication (ITD), a mutated receptor tyrosine kinase commonly found in patients with acute myelogenous leukemia (AML), led to the down-regulation of cyclin D2 and D3 followed by retinoblastoma protein (pRb) dephosphorylation and G(1) cell-cycle arrest. This implicated the D-cyclin-CDK4/6 complex as a downstream effector of Flt3 ITD signaling. Indeed, single-agent PD0332991, a selective CDK4/6 inhibitor, caused sustained cell-cycle arrest in Flt3 ITD AML cell lines and prolonged survival in an in vivo model of Flt3 ITD AML. PD0332991 caused an initial cell-cycle arrest in well-established Flt3 wild-type (wt) AML cell lines, but this was overcome by down-regulation of p27(Kip) and reactivation of CDK2. This acquired resistance was not observed in a Flt3 ITD and a Flt3 wt sample from a patient with primary AML. In summary, the mechanism of cell-cycle arrest after treatment of Flt3 ITD AML with a Flt3 inhibitor involves down-regulation of cyclin D2 and D3. As such, CDK4/6 can be a therapeutic target in Flt3 ITD AML but also in primary Flt3 wt AML. Finally, acquired resistance to CDK4/6 inhibition can arise through activation CDK2.

Differential apoptosis-inducing effect of quercetin and its glycosides in human promyeloleukemic HL-60 cells by alternative activation of the caspase 3 cascade

Flavonoids were demonstrated to possess several biological effects including antitumor, antioxidant, and anti-inflammatory activities in our previous studies. However, the effect of glycosylation on their biological functions is still undefined. In the present study, the apoptosis-inducing activities of three structure-related flavonoids including aglycone quercetin (QUE), and glycone rutin (RUT; QUE-3-O-rutinoside), and glycone quercitrin (QUI; QUE-3-O-rhamnoside) were studied. Both RUT and QUI are QUE glycosides, and possess rutinose and rhamnose at the C3 position of QUE, respectively. Results of the MTT assay showed that QUE, but not RUT and QUI, exhibits significant cytotoxic effect on HL-60 cells, accompanied by the dose- and time-dependent appearance of characteristics of apoptosis including an increase in DNA ladder intensity, morphological changes, apoptotic bodies, and an increase in hypodiploid cells by flow cytometry analysis. QUE, but not RUT or QUI, caused rapid and transient induction of caspase 3/CPP32 activity, but not caspase 1 activity, according to cleavage of caspase 3 substrates poly(ADP-ribose) polymerase (PARP) and D4-GDI proteins, and the appearance of cleaved caspase 3 fragments being detected in QUE- but not RUT- or QUI-treated HL-60 cells. A decrease in the anti-apoptotic protein, Mcl-1, was detected in QUE-treated HL-60 cells, whereas other Bcl-2 family proteins including Bax, Bcl-2, Bcl-XL, and Bag remained unchanged. The caspase 3 inhibitor, Ac-DEVD-FMK, but not the caspase 1 inhibitor, Ac-YVAD-FMK, attenuated QUE-induced cell death. Results of DCHF-DA assay indicate that no significant increase in intracellular peroxide level was found in QUE-treated cells, and QUE inhibited the H(2)O(2)-induced intracellular peroxide level. Free radical scavengers N-acetyl-cysteine (NAC) and catalase showed no prevention of QUE-induced apoptosis. In addition, QUE did not induce apoptosis in an mature monocytic cell line THP-1, as characterized by a lack of DNA ladders, caspase 3 activation, PARP cleavage, and an Mcl-1 decrease, compared with those in HL-60 cells. Our experiments provide evidence to indicate that the addition of rutinose or rhamnose attenuates the apoptosis-inducing activity of QUE, and that the caspase 3 cascade but not free radical production is involved.

Induction of phagocyte cytochrome b heavy chain gene expression by interferon gamma

Phagocytic cells, such as macrophages and polymorphonuclear leukocytes, produce a "respiratory burst" in which oxygen is reduced to superoxide and other active oxygen species responsible for many of the microbicidal, tumoricidal, and inflammatory activities of these cells. Interferon gamma has been shown to augment phagocyte superoxide production, but the molecular mechanisms underlying this effect have remained unknown. Recently a key component of the oxidase, phagocyte cytochrome b, has been characterized as a heterodimer of a 91-kDa glycoprotein and a 22-kDa polypeptide. The present studies examined the effects of human recombinant interferon gamma on the expression of the genes for these components of the cytochrome b. In vitro treatment with interferon gamma substantially increases the level of phagocyte cytochrome b heavy chain gene transcripts in normal polymorphonuclear leukocytes, normal monocyte-derived macrophages, and the monocytic leukemia cell line THP-1. Light chain gene transcripts are less affected. In monocyte-derived macrophages and THP-1 cells, the enhanced expression of the heavy chain gene appears in large part attributable to increased rates of transcription. Treatment of monocyte-derived macrophages with human recombinant interferon alpha (a down-regulator of the respiratory burst) decreased the heavy chain transcript levels; interferon beta produced no detectable change. These findings demonstrate the responsiveness of one essential component of the phagocyte oxidase system to activation by interferon gamma and provide a rationale for its use to augment phagocytic function in chronic granulomatous disease.

HoxA9-mediated immortalization of myeloid progenitors requires functional interactions with TALE cofactors Pbx and Meis

Specific Hox genes are implicated in leukemic transformation, and their selective genetic collaboration with TALE homeobox genes, Pbx and Meis, accentuates their oncogenic potential. The molecular mechanisms underlying these coordinate functions, however, have not been characterized. In this study, we demonstrate that HoxA9 requires its Pbx interaction motif as well as its amino terminus to enhance the clonogenic potential of myeloid progenitors in vitro. We further show that HoxA9 forms functional trimeric DNA binding complexes with Pbx and Meis-like proteins on a modified enhancer. DNA binding complexes containing HoxA9 and TALE homeoproteins display cooperative transcriptional activity and are present in leukemic cells. Trimeric complex formation on its own, however, is not sufficient for HoxA9-mediated immortalization. Rather, structure-function analyses demonstrate that domains of HoxA9 which are necessary for cellular transformation are coincident with those required for trimer-mediated transcriptional activation. Furthermore, the amino terminus of HoxA9 provides essential transcriptional effector properties and its requirement for myeloid transformation can be functionally replaced by the VP16 activation domain. These data suggest that biochemical interactions between HoxA9 and TALE homeoproteins mediate cellular transformation in hematopoietic cells, and that their transcriptional activity in higher order DNA binding complexes provides a molecular basis for their collaborative roles in leukemogenesis.

Regulation of tumor necrosis factor gene expression by ionizing radiation in human myeloid leukemia cells and peripheral blood monocytes

Previous studies have demonstrated that ionizing radiation induces the expression of certain cytokines, such as TNF alpha/cachectin. However, there is presently no available information regarding the molecular mechanisms responsible for the regulation of cytokine gene expression by ionizing radiation. In this report, we describe the regulation of the TNF gene by ionizing radiation in human myeloid leukemia cells. The increase in TNF transcripts by x rays was both time- and dose-dependent as determined by Northern blot analysis. Similar findings were obtained in human peripheral blood monocytes. Transcriptional run-on analyses have demonstrated that ionizing radiation stimulates the rate of TNF gene transcription. Furthermore, induction of TNF mRNA was increased in the absence of protein synthesis. In contrast, ionizing radiation had little effect on the half-life of TNF transcripts. These findings indicate that the increase in TNF mRNA observed after irradiation is regulated by transcriptional mechanisms and suggest that production of this cytokine by myeloid cells may play a role in the pathophysiologic effects of ionizing radiation.

Cbf beta-SMMHC induces distinct abnormal myeloid progenitors able to develop acute myeloid leukemia

The acute myeloid leukemia (AML)-associated CBF beta-SMMHC fusion protein impairs hematopoietic differentiation and predisposes to leukemic transformation. The mechanism of leukemia progression, however, is poorly understood. In this study, we report a conditional Cbfb-MYH11 knockin mouse model that develops AML with a median latency of 5 months. Cbf beta-SMMHC expression reduced the multilineage repopulation capacity of hematopoietic stem cells (HSCs) while maintaining their numbers under competitive conditions. The fusion protein induced abnormal myeloid progenitors (AMPs) with limited proliferative potential but leukemic predisposition similar to that of HSCs in transplanted mice. In addition, Cbf beta-SMMHC blocked megakaryocytic maturation at the CFU-Meg to megakaryocyte transition. These data show that a leukemia oncoprotein can inhibit differentiation and proliferation while not affecting the maintenance of long-term HSCs.

Quantitative single cell determination of ERK phosphorylation and regulation in relapsed and refractory primary acute myeloid leukemia

We investigated the constitutive activation of the MEK/ERK pathway in acute myelogenous leukemia (AML) via a flow cytometric technique to quantitate expression of phosphorylated ERK (p-ERK). A total of 42 AML samples (16 newly diagnosed, 26 relapsed/refractory) were analyzed. Normal bone marrow CD34+ cells (n = 10) had little or no expression of p-ERK, while G-CSF-mobilized CD34+ cells exhibited enhanced p-ERK levels. Markedly elevated p-ERK levels were found in 83.3% of the AML samples, with no differences observed between the newly diagnosed and relapsed/refractory samples. Treatment with a MEK inhibitor resulted in significantly decreased p-ERK levels in both the newly diagnosed and relapsed/refractory samples, which was associated with growth arrest, but not apoptosis induction. In summary, we defined conditions for the analysis of MAPK signaling in primary AML samples. Normal CD34+ cells expressed very low levels of p-ERK, and increased p-ERK levels were found in normal G-CSF-stimulated circulating CD34+ cells. Constitutively high p-ERK levels observed in the majority of AML samples suggest deregulation of this pathway that appears to be independent of disease status. The ability of ERK inhibition to promote growth arrest rather than apoptosis suggests that clinical trials of MEK/ERK inhibitors may be more effective when combined with chemotherapy.

Relationship of expression of aquaglyceroporin 9 with arsenic uptake and sensitivity in leukemia cells

Arsenic trioxide (As2O3) is highly efficacious in acute promyelocytic leukemia (APL). Aquaglyceroporin 9 (AQP9) is a transmembrane protein that may be involved in arsenic uptake. In 10 of 11 myeloid and lymphoid leukemia lines, quantitative polymerase chain reaction (Q-PCR) and Western blotting showed that AQP9 expression correlated positively with As2O3-induced cytotoxicity. As a proof-of-principle, transfection of EGFP-tagged AQP9 to the hepatoma line Hep3B, not expressing AQP9 and As2O3 insensitive, led to membrane AQP9 expression and increased As2O3-induced cytotoxicity. Similarly, the chronic myeloid leukemia line K562 expressed low levels of AQP9 and was As2O3 insensitive. The K562EGFP-AQP9 transfectant accumulated significantly higher levels of intracellular arsenic than control K562EGFP when incubated with As2O3, resulting in significantly increased As2O3-induced cytotoxicity. Pretreatment of the myeloid leukemia line HL-60 with all-trans retinoic acid (ATRA) up-regulated AQP9, leading to a significantly increased arsenic uptake and As2O3-induced cytotoxicity on incubation with As2O3, which might explain the synergism between ATRA and As2O3. Therefore, AQP9 controlled arsenic transport and might determine As2O3 sensitivity. Q-PCR showed that primary APL cells expressed AQP9 significantly (2-3 logs) higher than other acute myeloid leukemias (AMLs), which might explain their exquisite As2O3 sensitivity. However, APL and AML with maturation expressed comparable AQP9 levels, suggesting that AQP9 expression was related to granulocytic maturation.

JAK2 V617F is a rare finding in de novo acute myeloid leukemia, but STAT3 activation is common and remains unexplained

Signal transducer and activator of transcription (STAT) proteins are phosphorylated and activated by Janus kinases (JAKs). Recently, several groups identified a recurrent somatic point mutation constitutively activating the hematopoietic growth factor receptor-associated JAK2 tyrosine kinase in diverse chronic myeloid disorders - most commonly classic myeloproliferative disorders (MPD), especially polycythemia vera. We hypothesized that the JAK2 V617F mutation might also be present in samples from patients with acute myeloid leukemia (AML), especially erythroleukemia (AML-M6) or megakaryoblastic leukemia (AML-M7), where it might mimic erythropoietin or thrombopoietin signaling. First, we documented STAT3 activation by immunoblotting in AML-M6 and other AML subtypes. Immunoperoxidase staining confirmed phosphorylated STAT3 in malignant myeloblasts (21% of cases, including all AML-M3 samples tested). We then analyzed genomic DNA from 162 AML, 30 B-cell lymphoma, and 10 chronic lymphocytic leukemia (CLL) samples for JAK2 mutations, and assayed a subset for SOCS1 and FLT3 mutations. Janus kinase2 V617F was present in 13/162 AML samples (8%): 10/13 transformed MPD, and three apparent de novo AML (one of 12 AML-M6, one of 24 AML-M7, and one AML-M2 - all mixed clonality). FLT3 mutations were present in 5/32 (16%), while SOCS1 mutations were totally absent. Lymphoproliferative disorder samples were both JAK2 and SOCS1 wild type. Thus, while JAK2 V617F is uncommon in de novo AML and probably does not occur in lymphoid malignancy, unexplained STAT3 activation is common in AML. Janus kinase2 extrinsic regulators and other proteins in the JAK-STAT pathway should be interrogated to explain frequent STAT activation in AML.

Extracellular adenosine triphosphate activates calcium mobilization in human phagocytic leukocytes and neutrophil/monocyte progenitor cells

We have examined the ability of extracellular ATP to elicit intracellular Ca2+ mobilization in a broad range of human leukocytes at particular stages of hematopoietic differentiation. The average cytosolic [Ca2+] in various leukocyte populations was measured in Fura 2-loaded cell suspensions while the cytosolic [Ca2+] in individual, Indo 1-loaded leukocytes was assayed by flow cytometric methods. Utilizing normal blood- and marrow-derived cells, human leukemic cell lines, and mononuclear cell fractions derived from the blood of patients with various leukemias, we have found that ATP-induced Ca2+ mobilization appears restricted to leukocytes of neutrophil/monocyte ontogeny. Significant ATP-induced increases in cytosolic [Ca2+] were observed in neutrophils, monocytes, and myeloid progenitor cells as immature as myeloblasts, but not in lymphocytes. Extensive characterization of the ATP-induced changes in [Ca2+] observed in the HL-60 promyelocytic cell line have indicated these Ca2+-mobilizing effects of ATP can be correlated with an activation of inositol phospholipid breakdown via the occupation of P2-purinergic receptors Significantly, of the various agonists (FMLP, platelet-activating factor, LTB4, and ATP) which elicit equivalent and maximal Ca2+ mobilization in mature neutrophils and monocytes, ATP was the most efficacious stimulant of Ca2+ mobilization in immature neutrophil/monocyte precursors. Thus, expression of putative P2-purinergic receptors for ATP appears to precede expression of other receptor types known to activate the inositol phospholipid signaling cascades in terminally differentiated phagocytes.

RNA in human leukemic cells related to the RNA of a mouse leukemia virus (leukocytes-RNA-DNA hybridization-rauscher virus-polysomal RNA)

Molecular hybridization with radioactively labeled DNA complementary to the RNA of the Rauscher leukemia virus was used to probe for homologous RNA in the polysome fraction of human leukemic cells. The leukocytes of 24 out of 27 patients examined contained RNA possessing homology to that of the mouse leukemia agent, but not to that of the unrelated viruses causing mammary tumors in mice or myeloblastosis in chickens. Further, no control human leukocytes or other adult and fetal tissues showed significant levels of the leukemia-specific RNA. It would appear that human leukemic cells contain RNA sequences homologous to those found in a viral agent known to cause leukemia in an experimental animal. The fact that human sarcomas have also been shown to contain this type of RNA points to a remarkable parallelism in the leukemias and sarcomas of mice and men.

Transformation of myeloid leukemia cells to cytokine independence by Bcr-Abl is suppressed by kinase-defective Hck

Bcr-Abl is the constitutively active protein-tyrosine kinase expressed as a result of the Philadelphia translocation in chronic myelogenous leukemia. Bcr-Abl is coupled to many of the same signaling pathways normally regulated by hematopoietic cytokines. Recent work shows that Hck, a member of the Src tyrosine kinase family with myeloid-restricted expression, associates with and is activated by Bcr-Abl. Here we investigated the mechanism of Hck interaction with Bcr-Abl and the requirement for Hck activation in Bcr-Abl transformation signaling. Binding studies demonstrated that the Hck SH3 and SH2 domains are sufficient for interaction with Bcr-Abl in vitro. Hck binding localizes to the Abl SH2, SH3, and kinase domains as well as the distal portion of the C-terminal tail. To address the requirement for endogenous Src family kinase activation in Bcr-Abl signaling, a kinase-defective mutant of Hck was stably expressed in the cytokine-dependent myeloid leukemia cell line DAGM. Kinase-defective Hck dramatically suppressed Bcr-Abl-induced outgrowth of these cells in the absence of cytokine compared with a control cell line expressing beta-galactosidase. In contrast, kinase-defective Hck did not affect cell proliferation in response to interleukin-3, suggesting that the effect is specific for Bcr-Abl. These data show that Hck interacts with Bcr-Abl through a complex mechanism involving kinase-dependent and -independent components and that interaction with Hck or other Src family members is essential for transformation signaling by Bcr-Abl.

Expression of Functional B7-H2 and B7.2 Costimulatory Molecules and Their Prognostic Implications in De novo Acute Myeloid Leukemia

PURPOSE

The B7 family molecules have been shown to regulate immune responses in both positive and negative fashions. Their roles in the progression of human cancers, however, are not well established. The aim of this study was to examine whether leukemic cells of acute myeloid leukemia express functional B7 family molecules and, if so, whether such expression has any clinical significance.

EXPERIMENTAL DESIGN

The expression of four B7 family molecules, B7.1, B7.2, B7-H1, and B7-H2, on leukemic cells from acute myeloid leukemia patients was analyzed by flow cytometry. The function of the expressed molecules was examined by the allogeneic mixed lymphocyte-leukemic cell reaction, and their relationship to the clinical data and survival was analyzed.

RESULTS

Although B7.1 and B7-H1 expressions were rare, the cells from a substantial number of acute myeloid leukemia cases expressed B7.2 and B7-H2 molecules [mean percentages of B7.2- and B7-H2-positive cells were 28.9% (n = 58) and 15.3% (n = 59), respectively]. Patients in whom >25% of leukemic cells expressed B7-H2 had significantly shorter survival, and this B7-H2 positivity had the strongest prognostic value when B7-H2 and other prognostic factors were analyzed together by multivariate analysis (P = 0.0108). Furthermore, B7.2 expression was associated with hyperleukocytosis (P = 0.026). Consistent with this finding, acute myeloid leukemia cells expressing B7.2 and B7-H2 induced allogeneic CD4+ T cells to proliferate and secrete interleukin-4 and interleukin-10 in vitro, effects that were partially blocked by antibodies against B7.2 and B7-H2.

CONCLUSIONS

Our results indicate the expression of functional B7.2 and B7-H2 molecules, and these molecules may facilitate progression of acute myeloid leukemia.

Characterization of the cell surface receptor for human granulocyte/macrophage colony-stimulating factor

125I-labeled recombinant human GM-CSF was used to identify and characterize receptors specific for this lymphokine on both a mature primary cell, human neutrophils, and on the undifferentiated promyelomonocytic leukemia cell line, HL-60. Human GM-CSF also bound to primary human monocytes and to the myelogenous leukemia cell line, KG-1, but not to any of the murine cells known to express the murine GM-CSF receptor. In addition, although some murine T lymphomas can express the GM-CSF receptor, none of the human cell lines of T cell lineage that we examined bound iodinated human GM-CSF. Binding to all cell types was specific and saturable. Equilibrium binding studies revealed that on all cell types examined, GM-CSF bound to a single class of high affinity receptor (100-500 receptors per cell) with a Ka of 10(9)-10(10)/M. More extensive characterization with neutrophils and HL-60 cells showed that in both cases, binding of GM-CSF was rapid at 37 degrees C with a slow subsequent dissociation rate that exhibited marked biphasic kinetics. Among a panel of lymphokines and growth hormones, only human GM-CSF could compete for binding of human 125I-GM-CSF to these cells. GM-CSF can not only stimulate the proliferation and differentiation of granulocyte/macrophage precursor cells, but can modulate the functional activity of mature granulocytes and macrophages as well. No significant differences in the kinetic parameters of receptor binding were seen between mature neutrophils and the undifferentiated promyelocytic leukemia cell line HL-60, indicating that maturation-specific responses to GM-CSF are not mediated by overt changes in the binding characteristics of the hormone for its receptor.

Restoration of daunomycin retention in multidrug-resistant P388 cells by submicromolar concentrations of SDZ PSC 833, a nonimmunosuppressive cyclosporin derivative

Overexpression of P-glycoprotein may cause increased efflux of a variety of anticancer drugs (ACD) leading to multidrug resistance (MDR) of tumor cells. Two sublines of murine monocytic leukemia P388 cells were used, one parental (Par-P388) and one multidrug resistant (MDR-P388). In cell growth inhibition assays in vitro, the Par-P388 cells showed a normal sensitivity to daunomycin (DAU) while the MDR-P388 cells were 200-fold resistant. In cellular fluorescence assays, DAU retention in MDR-P388 cells reached only 5% of the level achieved in Par-P388 cells. This cell line pair was used to compare the nonimmunosuppressive cyclosporin analog PSC 833 with several resistance-modifying agents (RMAs) for their in vitro chemosensitizing activity and for their restoration of DAU retention. PSC 833 sensitized the MDR-P388 cells 60- and 140-fold when used at 0.1 and 0.3 micrograms/ml (0.08 and 0.25 microM), respectively, a complete restoration of sensitivity being obtained at 1.0 micrograms/ml PSC 833. Similarly as little as 0.1 micrograms/ml (0.08 microM) PSC 833 was sufficient to restore intracellular DAU retention to 60% of the level found in Par-P388 cells, a 3-fold higher concentration restoring virtually the whole DAU retention. For both these activities, PSC 833 was at least one order of magnitude more active than CsA, which was itself an order of magnitude stronger than verapamil, another RMA already used in clinic. Since PSC 833 had no effect on the PAR-P388 cells, neither on chemosensitization nor on drug retention, it is assumed that it acts on the P-glycoprotein, which is highly expressed on the membrane of the MDR-P388 cells, by inhibiting the function of the P-glycoprotein pump and thus restoring a normal ACD-sensitivity of the MDR-P388 cells.